In rapid progress of trend of smaller size and higher performance of electronic appliances such as cellphones, recently, the withstand voltage of the electronic components used in the electronic appliances tends to be lower. Accordingly, there is an increasing number of breakdown accidents of electric circuits inside the appliance due to electrostatic discharge pulse caused by contact between part of human body and terminal of electronic appliance. When electrostatic discharge is generated, a high voltage of a bout hundreds of volts to several kilovolts is generated and applied to the electronic appliance in a scant moment of 0.5 to 2 nanoseconds.
Hitherto, as measure against such electrostatic discharge pulse, it has been proposed to bypass the electrostatic discharge by disposing a varistor or zener diode between the incoming line of electrostatic discharge and the ground, and to suppress the voltage applied to the electric circuit of the appliance.
Moreover, as disclosed in Japanese Laid-open Patent No. S63-56023, in a satellite broadcast receiving apparatus comprising a plane antenna for satellite broadcast not grounded in direct current, and a converter connected to the plane antenna by way of a transmission line having an amplifying circuit in a front stage, a filter circuit composed of an inductive element for connecting the transmission line and the ground, and a capacitive element connected to a rear stage of the connection point of the inductive element and transmission line is provided between the plane antenna and the amplifying circuit, thereby preventing damage by electrostatic discharge. An air gap coil is used as the inductive element, and a capacitor is used as the capacitive element.
However, if attempted to suppress the voltage applied to the electric circuit of the appliance by bypassing the electrostatic discharge by using the varistor or zener diode or in the disclosed method, since the reaction speed of the elements such as varistor or zener diode to the electrostatic discharge pulse is slow, sufficient bypassing effect is not obtained. Although somewhat different depending on the size or composition of the elements, electrostatic discharge occurring in about 0.5 to 2 nanoseconds cannot be bypassed sufficiently. Therefore, existing protection components cannot suppress sufficiently the highest peak voltage in about 0.5 to 2 nanoseconds occurring as electrostatic discharge, and it has been difficult to prevent breakdown of electronic components or electronic appliances securely. However, when a varistor or zener diode of very high capacity such as several nF unit or more is used, peak voltage of about 0.5 to 2 nanoseconds may be suppressed to a certain extent. But such element cannot be used in a high speed transmission circuit of more than tens of MHz units.